1. Technical Field
The invention relates to dispensing devices for dispensing and mixing plural component flowable materials. More particularly, the invention relates to a dispensing device and method which provides a positive shut-off or snuff back of the flowable material to prevent drippage of the material from the device when the device is in the off position and to a device and method which provides for the dynamic mixing of the two materials as they move through a mixing tube.
2. Background Information
An ever increasing number of products used in everyday life require the dispensing of liquid or semi-liquid flowable materials in one form or another for their manufacture. These flowable materials typically comprise two component reactive resins. The types of materials dispensed include virtually any flowable liquid, semi-liquid, or paste such as epoxies, polyurethanes, silicones, polyester, acrylics, polysulfides and phenolic, for example. Common commercial manufacturing processes in which such materials are used include injecting precise amounts of mixed resins into molds, open pouring of mixed foam, encapsulating electric components with insulating resins, applying continuous beads of structural adhesives, injecting polyester into closed molds, sealing joints with two part polysulfides, and numerous other functions requiring the accurate control, delivery and mixing of two reactive component materials. Examples of product application include air filters, under the hood electronic assemblies and safety devices for the automotive and trucking industry, air foils, encapsulation of magnetic and other advanced electrical devices for the air and space industry, component mounting, and components for apparatus such as switches, power supplies, heating assemblies, and other electronic components for the appliance industry.
Thus, as the aforesaid flowable mixed materials continue to be consumed in increasing quantities, the demand for precise liquid and semi-liquid, mixing and dispensing devices is also growing at an accelerated rate. The industry is continuously searching for more reliable, efficient and accurate, mixing and dispensing devices for plural component flowable materials for a variety of purposes. For example, a particular application may require that a device efficiently and accurately dispenses such plural materials ranging in amounts from less than 1 cubic centimeter to many gallons. However, although the industry is calling for more exact device, it is also requiring that the device design be simple and minimize waste, and capable of being operated by production personnel or conveniently integrated with automation devices such as robots and conveyor systems.
Problems currently exist because many prior art plural component mixing and dispensing devices permit small amounts of the mixed material to leak or drip from the outlet end of a mixer tube after the control valves within the device have been moved to an off position. This is unacceptable in many production applications. Another problem with prior art mixing and dispensing devices, especially those using a motionless mixer mounted within a mixer tube, such as shown in U.S. Pat. No. 5,092,492, is that the two materials are not mixed sufficiently as they move through the mixing elements. Furthermore, the rate of mixing and dispensing can be adversely effected by the back pressure created within such a motionless mixing element.
Some examples of mixing and dispensing devices for two component liquid materials are shown in U.S. Pat. Nos. 5,092,492 and 5,350,084. Other types of dispensing and metering devices only dispense a single material such as shown in U.S. Pat. Nos. 3,806,084; 4,095,722; and 4,942,984. However, these devices will not use a motionless type of mixer at the outlet end of the device and thus do not encounter the same problems as those devices which meter and dispense two component materials.
Therefore, the need exists for an improved liquid mixing and dispensing device in which plural component materials are mixed adjacent to the point of dispensing, in a helical type mixing element, which device provides for the positive stopping of the mixed materials to prevent dripping when the feed control valves are shut off, and to a device which can rotate the heretofore motionless mixing element to enhance the mixing of the plural components.